Capitalism has a deep-seated taboo against taking recreational drugs. So strong is the taboo they will ruin your life and exile you from mainstream society for doing something recreational.
This is changing a bit as the scientists tell them there is basically no reason for this. But the scientists meet with resistance from entrenched cops, judges, lawyers, who are very 
about it.
What's the materialist explanation for this moralistic taboo?
In the US more people than any any other state in history (save for the worst period of Nazi Germany) are kept as basically slaves in jails and prisons on drug charges and they are loaned out to capitalists. A significant section of the underclass is held down by drug use where they are sedated both personally and politically, forced into the worst jobs, or the reserve army of labor.
This isn't a conspiracy though. Like the prisons aren't conspiring with the cartels. It's all just capitalists trying to make money by screwing someone else over and seeing both extremely vulnerable drug producers and drug users and taking advantage of them. Capitalism rewards this so it's reproduced until it isn't possible to squeeze any more juice out of it.